The present invention relates to an integrated circuit device, and relates in particular to an integrated circuit device having multiplexed oscillators.
Integrated circuit devices require a high level of functional safety. In-vehicle ICs (integrated circuits) for example require a high level of functional safety, and functional safety relating to automobile electrical and electronic functions are established as an international standard in ISO26262.
Functional safety generally includes the following stages. Stage 1: detect abnormalities and stop operation. Stage 2: Maintain operation by switching to a correctly operating circuit when an abnormality is detected. Manufacturers of automobiles and electrical equipment are currently proceeding to achieve stage 1 while aiming to attain stage 2 in the future and to achieve those functions.
Amidst these circumstances, in-vehicle IC is also currently required to have functional safety when an abnormality occurs in the internal circuits. Progress is being made among in-vehicle IC for example towards (circuit) redundancy and so on, with designs that stop operation if there is an abnormality in one (circuit). Moreover, even higher safety performance is being demanded for in-vehicle IC and the goal is to achieve the second stage.
The oscillator is one of the main elements in the integrated circuit and demands are also being made for functional safety in the oscillator. This state has led to proposals for semiconductor devices configured from multiplexed oscillators.
A multiplexed timer device containing three oscillators for example is disclosed in Japanese Unexamined Patent Application Publication No. 2006-252086. The multiplexed timer device disclosed in this publication contains three oscillators and three timer counters coupled to the respective oscillators. The timer device is designed to compare the count values from each of the timer counters with an average count value for the three timer counters, and select the count value nearest the average value for use as a timer output signal. The timer device is capable of detecting a breakdown or lower accuracy in one timer counter, and also utilizing the timer counter among the three timer counters having the highest accuracy to continue operation.
The above multiplexed timer device however operates by comparing the count value with the average value so that the structure requires three or more oscillators. This larger number of oscillators is not preferable due to the resulting increased circuit scale.
A technology on the other hand disclosing an information processing device having a multiplexed clock system utilizing two oscillators is disclosed in Japanese Unexamined Patent Application Publication No. 2010-205154. The information processing device in this publication contains two clock boards respectively including the clock source, and a plurality of system boards. One of the two clock boards is utilized to generate operation clock (pulses) and other clock board is utilized to generate standby clock. These generated operation clocks and standby clocks are supplied to each system board. Each system board contains a clock detector circuit to detect whether or not operation clocks are being supplied. When the clock detector circuit detects that there are no operation clocks (or stoppage of the operation clock), the information processing device switches the clock being used from the (current) operation clock to the standby clock.